1. Field of the Invention
The present invention relates to a lighting apparatus and a calibration method therefor.
2. Description of the Related Art
In general, a color image display apparatus includes a color liquid crystal panel having light filters, and a backlight apparatus which is alighting apparatus for irradiating white light to a back surface of the color liquid crystal panel.
In the past, as light sources for backlight apparatus, fluorescent lamps such as cold cathode fluorescent lamps (CCFL: Cold Cathode Fluorescent Lamps), etc., have mainly been used. However, in recent years, light emitting diodes (LED: Light Emitting Diodes), which are advantageous in respect of electric power consumption, life span, color reproducibility, and environmental impact, are becoming increasingly used as light sources of backlight apparatus.
A backlight apparatus using LEDs as a light source (LED backlight apparatus) is generally composed of a lot of LEDs. Japanese patent application laid-open No. 2001-142409 discloses an LED backlight apparatus which is constructed such that it is divided into a plurality of light emission blocks, each of which is composed of one or more LEDs, wherein brightness control is carried out on these light emission blocks independently of one another. The electric power consumption of the LED backlight apparatus is decreased and the contrast of an image is improved, by reducing the brightnesses of those light emission blocks which irradiate light on those areas of a color liquid crystal panel in which a dark image is displayed, among all the display areas thereof. Such brightness control for each light emission block according to the content of a displayed image is referred to as local dimming control.
On the other hand, when brightness control for each light emission block is carried out by means of local dimming control, there will be a problem of unevenness in brightness of the LED backlight apparatus as a whole. One factor for this problem is that temperature variation among the light emission blocks is caused by the brightness control for each light emission block, so that the brightness of each light emission block varies due to the temperature characteristics of the LEDs. Another factor is that variation in the extent of aged deterioration among the light emission blocks is caused due to the brightness control for each light emission block, thus resulting in brightness variation.
As a technique of reducing the brightness unevenness generated due to such variation in temperature among the light emission blocks and in the extent of aged deterioration, there is known a technique of detecting and correcting the brightness of each light emission block by means of an optical sensor in a state where the individual light emission blocks are caused to turn on in a sequential manner.
In international laid-open publication No. 2008/029548, the time required to carry out the calibration of an LED backlight apparatus is made shorter, by detecting the brightnesses of individual light emission blocks at the same time with the use of a plurality of optical sensors in a state where the plurality of light emission blocks, which are arranged at an interval d apart from each other, are caused to turn on at the same time.